The present invention relates to improvements in a method for constructing a tunnel.
The inventor of this invention proposed, in Japanese Patent Publication No. 54-33656, a method for constructing a tunnel consisting of the steps of assembling an inner form within a tunnel bore that has been successively dug by means of a shield tunnelling machine, placing concrete in a space delimited by the form, a shield tail and a front surface of an already placed concrete lining, and thereafter shoving the shield tunnelling machine by means of a concrete lining jack and a shield jack equipped on the shield tunnelling machine with shoving reaction forces received by the placed concrete and the inner form.
In soft ground to which a shield tunnelling method is applied for constructing a tunnel, it is necessary to employ a reinforced concrete structure to assure safety of the tunnel body structure. Accordingly, upon practicing the above-mentioned constructing method in the prior art, it is necessary to set a reinforcing steel cage within the shield tail of the shield tunnelling machine and to dispose it at a predetermined position.
However, in the shield tail section, working space is very narrow, so the work for assembling the reinforcing steel cage becomes complex, and moreover it is difficult to dispose the set reinforcing steel cage at a predetermined position. Furthermore, upon compressing the placed concrete, there is a fear that the reinforcing steel cage may be moved or deformed. Therefore, it becomes impossible to realize the function of a desired reinforced concrete structure.